Or HaChaim on Genesis 50:15/אור החיים על בראשית נ׳:ט״ו

1 לו ישטמנו יוסף, "perhaps Joseph will hate us, etc." In this instance the word לו means "perhaps," though there is no other such instance in the Torah where the word לו is used in that sense. We need to understand why the Torah uses the word לו here in a sense which is the opposite of its regular meaning. Although it is quite impossible to mistake the meaning of this word in our context, why did the Torah not use such words as פן, or אולי if the intention was to describe the brothers as saying "perhaps?"

2It seems that the Torah has the brothers express a subconscious desire for Joseph to pay them back for all they had done to him. If Joseph were to do that now and the brothers would experience a similar agony to that which they had subjected him to, they would no longer have to worry about paying for their sin against him at the end of the exile. Yalkut Mishley 929 describes that the 10 martyrs executed by Hadrian were in retribution for the failure to punish the brothers who had sold Joseph at the time. Shabbat 10 attributes the exile in Egypt to the coloured coat Jacob had made for Joseph and which resulted in the jealousy of his brothers.